The invention relates to devices and a method especially adapted for conveying hard particulate material, the particles having non-uniform and irregular shapes, such as coal. An especially desirable system and method for conveying such material hydraulically is illustrated and described in U.S. Pat. No. 4,082,368. In that patented system, a high pressure transfer device is utilized for boosting the pressure of the hydraulically conveyed material to effect conveyance thereof along a pipeline and/or from underwater mine sites.
While the system described in the patent is very effective for accomplishing its desired end results, it has been discovered that during use of the system excessively great wear of the screen associated with the high pressure transfer device occurs. In particular, it has been discovered that large grooves are formed in the transverse bars mounting the spaced, elongated bars forming the screen, at one end thereof, the grooves being formed exceptionally quickly so that the apparatus must be shut down and the screens replaced with undesired frequency. According to the present invention it has been determined that the source of the screen wearing problem is the lodging of irregular pieces of the hard material such as granite, basalt, quartz, etc. being conveyed in the screen slots, such lodged pieces being carried along the slots by the rotor of the high pressure transfer device to the ends of the slots, and causing abrading thereof before the particles are broken up.
According to the present invention, a method and apparatus are provided for eliminating the screen wearing problem that occurs in the conveyance of hard particulate material, as discussed above with respect to U.S. Pat. No. 4,082,368 (the disclosure of which is hereby incorporated by reference herein).
According to the method of the present invention, hard particulate material, the particles having non-uniform and irregular shapes, such as coal, is continuously conveyed utilizing a high pressure transfer device including a pocketed rotor containing a pair of diametrically through-going pockets perpendicular to each other, a housing enclosing the rotor and having four ports equally spaced around the periphery thereof for registry with inlets and outlets from the through-going pockets and the rotor, and a screen associated with the housing and rotor for allowing passage of liquid and particles smaller than a predetermined size therethrough, but preventing passage of particles larger than the predetermined size therethrough. Liquid containing the hard particulate material is continuously fed into a first of the housing ports for entry into a through-going pocket of the rotor. The rotor is rotated in a given direction of rotation so that it rotates past each of the housing ports. Withdrawal of liquid introduced through the first port is provided from through-going pockets of the rotor through a third port of the housing, opposite the first port, screening of the particulate material above a predetermined size out of the liquid passing through the port being practiced utilizing the screen. Liquid under high pressure is pumped toward the rotor through a fourth port of the housing, the fourth port being located between the third and first ports in the direction of rotation of the rotor, and withdrawal of liquid is provided through a second port located opposite the fourth port, without screening of the liquid. Prevention of damage to the screen as a result of particles of the hard particulate material being trapped therein and carried along the screen by the rotor into abrading contact with solid portions of the screen is positively prevented. This positive prevention is accomplished in one of two ways: by injecting fluid under pressure into the screen to effect dislodgement of particles that may be lodged in the screen; or by providing a screen interiorly of each of the through-extending pockets, between the inlet and outlet of each pocket.
When prevention of damage to the screen is practiced by injecting fluid under pressure to dislodge particles from the screen, the device according to the invention that is utilized preferably includes a screen having a plurality of elongated bars, elongated in the direction of rotation of the rotor, and means for maintaining the bars in parallel spaced relationship, being spaced in a dimension parallel to the axis of rotation of the rotor. A plurality of fluid injection nozzles are mounted in one of the transverse bars forming the elongated bar supporting means, and the screen is mounted in the third port of the housing. A header may be provided in the transverse bar to which each of the fluid injecting nozzles is connected, each nozzle pointing upwardly towards the tops of the bars in the space between adjacent bars, to effect dislodgement of particles back into a pocket of the rotor. Operation of the fluid injection means is timed to the rotation of the rotor, such as by mounting a cam for rotation with the rotor, and utilizing a linearly movable cam follower for engaging the cam, and means responsive to the linear motion of the cam follower for effecting operation of a valve to supply fluid (preferably liquid) under pressure to the fluid injection nozzles. The transverse bar of the screen with which the fluid injection means is associated provides a rearmost portion of the screen, in the direction of rotation of the rotor, the timing being gauged so that fluid is injected only when a trailing edge, in a direction of rotation of the rotor, of a through-going pocket in the rotor approaches the rearmost portion of the screen.
When the damage prevention to the screen is accomplished by mounting a screen interiorly of each of the through-extending pockets, preferably the pockets are dimensioned so that they are much wider at a middle portion thereof than at the inlets and outlets. The screen in such a situation preferably comprises a plurality of bars that are square or circular in cross-section with means for mounting the bars so that they are parallel to each other and spaced apart in a dimension perpendicular to the direction of flow of liquid through the pockets, and so that the present the same surface configuration or circular to the liquid flowing through the pockets in either direction.
It is the primary object of the present invention to provide an improved device and method for conveying hard particulate material so that screen damage is minimized. This and other objects of the invention will become clear from an inspection of the detailed description of the invention, and from the appended claims.